In recent years, LEDs are often used for automotive lighting. The flexible printed board is often used as a printed board for lighting using the LED. The LED is mounted on the flexible printed board. Therefore, the LED cannot be replaced. Therefore, improvement of heat dissipation performance of the flexible printed board is required to extend the life of the LEI).
An example of satisfying this requirement is a structure (referred to as an aluminum bonded substrate) in which an expensive aluminum heat dissipating material made of aluminum is bonded to a flexible printed board. Further, there is also the aluminum bonded substrate in which the above-described aluminum heat dissipating material is processed into a three-dimensional shape in order to further improve the heat dissipation performance. In the aluminum bonded substrate having such a structure, the heat dissipation performance is improved by bonding the aluminum heat dissipating material. However, there is a problem that the price of the aluminum heat dissipating material is higher than the cost required for the material or processing of the flexible printed board. Further, devices are required to be lightweight in automotive lighting. However, such a structure in which a large number of such an aluminum heat dissipating material is bonded is contrary to such a demand for weight reduction.
As a countermeasure for such a problem, there is a structure disclosed in PATENT LITERATURE 1. In the structure disclosed in PATENT LITERATURE 1, since the aluminum heat dissipating material is not used, the weight reduction can be achieved.